Analog signal is widely used in industrial automation for applications such as measurement input, analog control. In later 80s', HART (Highway Addressable Remote transducer) protocol adds frequency signal in the analog signal which enhances the use of analog signal to high level industrial automation like intelligent instrument and asset management. Such important usage as well as harsh industrial environment needs higher requirement for both signal accuracy and isolation for transmitting the analog signal.
There are three ways of analog signal isolation for now. The first is to use isolated switch (PhotoMos) which has high voltage withstand, the second is to use isolated linear amplifier with normal analog switch and the last is to use transformer with better linearity together with normal analog switch. All these methods can isolate analog signal and transfer signal with high linearity. Not to mention all of the components used in these methods are quite expensive, they are also relatively large and not suitable for minimizing product size.